Power control is an important functionality used in the air interface of a radio system using Code Division Multiple Access (CDMA). Power control is used to continuously adjust transmission power such that the perceived quality is sufficiently but not excessively good. The aim is to ensure that not more than necessary interference is generated, thereby improving the overall system performance.
There are two power control loops, the inner loop and the outer loop. The outer loop power control is adapted to adjust the Signal to Interference plus Noise Ratio (SINR) target so that the desired Quality of Service (QoS) requirement is met. The inner loop power control adjusts transmission power so that the SINR perceived by the receiver is close to the SINR target. The power control is implemented by sending power control commands via so called Transmission Power Control (TPC) bits. To increase power the TPC bit indicates “up” and to decrease the power the TPC bit indicates “down”. The power control command is obtained by comparing the received SINR with the SINR target.
The convergence of inner loop power control can be further improved by e.g. utilizing the previous power control commands at either the transmitter or the receiver. More specifically,                Utilizing the already generated power control commands at the transmitter could help to compensate the time delay in the power control loop, see Fredrik Gunnarsson, Fredrik Gustafsson, “Time Delay Compensation for CDMA Power Control” and the international patent application No. WO 01/03329 A1, which may range from 2 or 3 time slots to 7 or 8 time slots.        Utilizing the already received power control commands at the receiver this could help to realize the adaptive adjustment of inner loop power control step size, see Jad Nasreddine, Louffi Nuagmi and Xavier Lagrange, “DOWNLINK ADAPTIVE POWER CONTROL ALGORITHM FOR 3G CELLULAR CDMA NETWORKS.”        
It has been shown that both of the improvements can decrease the SINR oscillations around the SINR target and thus lead to improved performance, by allowing for decreased mobile station transmission power and consequently decreased interference. This is in particular so for mobile stations, which are not in soft handover, i.e. the mobile stations that are only connected to one base station and solely power controlled by that base station. However, the situation during soft handover may be different. A mobile station in soft handover is connected to two or more base stations and may be power controlled by any of the connected base stations. Each connected base station transmits its own power control command to the mobile station, and the mobile station combines the received power control commands in the following way:                A power increase only if all the power control commands indicate “up”        Otherwise power is decreased.        
This implies that when more than one base station power controls a mobile station neither of the base stations to which the mobile station is connected, can know that the mobile station follows its power control command, and utilizing already generated power control commands at the base stations cannot help to improve the convergence of inner loop power control. There are some ways to solve this:                Do not utilize the already generated power control commands at the base stations when a mobile station is in soft handover, see Fredrik Gunnarsson, Fredrik Gustafsson, “Time Delay Compensation for CDMA Power Control.”        Utilize other measures at the base stations which are valid in soft handover as well, i.e. even the base station cannot make sure that if its power control commands are followed by the connected mobile station, to improve the inner loop power control converge. One such measure is the most recent received signal code power (RSCP).        
However, simply disabling the utilization of the already generated power control commands at the base stations in soft handover has a drawback because mobile stations in soft handover cannot compensate the time delay in their power control loop and thus have larger SINR and consequently also power oscillation. Typically there is around 20% to 30% mobile stations in soft handover, and it is mainly the mobile stations around cell border that are in soft handover, which have relatively high power and generate relatively high interference. It is therefore probably more important to improve the power control performance for mobile stations in soft handover.
Some measures, e.g. the most recent RSCP at the base station, are valid no matter whether the base station is in soft handover or not. However, the solutions based on this measure also have some drawbacks, including:                It can only compensate the generating delay but not the transmitting delay in power control commands. This is because RSCP can only reflect the effect of the power control commands that are already applied at the mobile station, but not the effect of the power control commands that are already generated but not yet applied at the mobile station, see Jad Nasreddine, Louffi Nuagmi and Xavier Lagrange, “DOWNLINK ADAPTIVE POWER CONTROL ALGORITHM FOR 3G CELLULAR CDMA NETWORKS.”        There exists estimation error in RSCP estimation, and in some cases this error may become relatively large, e.g. when sequential interference cancellation (SIC) is applied. This is because SIC introduces additional processing delay, and to compensate for this delay we need to adopt the RSCP estimation before SIC, which suffers from higher interference and is thus more unreliable, see Fredrik Gunnarsson, “Uplink Sequential IC and Power Control Behavior,” EAB-08:039083.        
The benefit from the RSCP based solution is less than that from the power control commands based solution when e.g. the base station is not in soft handover.
Hence, there exist a need for a method and a system that is able to provide an improved power control for soft handover in a cellular radio system.